linux-kernel - Re: [PATCH 4.4 30/30] mm: larger stack guard gap, between vmas

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Date:   Tue, 20 Jun 2017 22:41:01 -0700 (PDT)
From:   Hugh Dickins <hughd@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Hugh Dickins <hughd@...gle.com>,
        Michal Hocko <mhocko@...e.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Willy Tarreau <w@....eu>
Subject: Re: [PATCH 4.4 30/30] mm: larger stack guard gap, between vmas

On Mon, 19 Jun 2017, Greg Kroah-Hartman wrote:

> 4.4-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Hugh Dickins <hughd@...gle.com>
> 
> commit 1be7107fbe18eed3e319a6c3e83c78254b693acb upstream.

The 4.11 and 4.9 patches are fine, but I noticed a couple of corrections
to this 4.4 one.  There are very unlikely circumstances (on VM_GROWSUP
architectures only) in which that "highest_vm_end = end" line would be
wrong: several different ways to fix it, I'm tending to go with Andrea's
observation that the only need for update has already been done above,
so just VM_WARN_ON if it's unexpected.

Hugh

diff -purN 404n/include/linux/mm.h 404h/include/linux/mm.h
--- 404n/include/linux/mm.h	2017-06-20 16:48:17.162770068 -0700
+++ 404h/include/linux/mm.h	2017-06-20 17:36:35.871975695 -0700
@@ -1283,6 +1283,8 @@ static inline bool vma_is_anonymous(stru
 	return !vma->vm_ops;
 }
 
+int vma_is_stack_for_task(struct vm_area_struct *vma, struct task_struct *t);
+
 extern unsigned long move_page_tables(struct vm_area_struct *vma,
 		unsigned long old_addr, struct vm_area_struct *new_vma,
 		unsigned long new_addr, unsigned long len,
diff -purN 404n/mm/mmap.c 404h/mm/mmap.c
--- 404n/mm/mmap.c	2017-06-20 16:48:17.166770032 -0700
+++ 404h/mm/mmap.c	2017-06-20 17:42:31.312682716 -0700
@@ -923,7 +923,7 @@ again:			remove_next = 1 + (end > next->
 		else if (next)
 			vma_gap_update(next);
 		else
-			mm->highest_vm_end = end;
+			VM_WARN_ON(mm->highest_vm_end != vm_end_gap(vma));
 	}
 	if (insert && file)
 		uprobe_mmap(insert);